In the asynchronous setting, distributed behavior is traditionally studied through computa- tions, the Happened-Before posets of events generated by the system. An equivalent perspective considers the linear extensions of the generated computations: each linear extension defines a sequence of events, called an execution. Both perspective were leveraged in the study of asyn- chronous point-to-point message orderings over computations; yet neither allows us to interpret message orderings defined over executions. Can we nevertheless make sense of such an ordering, maybe even use it to understand asynchronicity better? We provide a general answer by defining a topology on the set of executions which captures the fundamental assumptions of asynchronicity. This topology links each message ordering over executions with two sets of computations: its closure, the computations for which at least one linear extension satisfies the predicate; and its interior, the computations for which all linear ex- tensions satisfy it. These sets of computations represent respectively the uncertainty brought by asynchronicity – the computations where the predicate is satisfiable – and the certainty available despite asynchronicity – the computations where the predicate must hold. The paper demon- strates the use of this topological approach by examining closures and interiors of interesting orderings over executions.
@InProceedings{shimi_et_al:LIPIcs.OPODIS.2017.29, author = {Shimi, Adam and Hurault, Aur\'{e}lie and Qu\'{e}innec, Philippe}, title = {{Asynchronous Message Orderings Beyond Causality}}, booktitle = {21st International Conference on Principles of Distributed Systems (OPODIS 2017)}, pages = {29:1--29:20}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-061-3}, ISSN = {1868-8969}, year = {2018}, volume = {95}, editor = {Aspnes, James and Bessani, Alysson and Felber, Pascal and Leit\~{a}o, Jo\~{a}o}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2017.29}, URN = {urn:nbn:de:0030-drops-86387}, doi = {10.4230/LIPIcs.OPODIS.2017.29}, annote = {Keywords: Asynchronous computations, Point-to-point message orderings, Causality, Topology, Interior, Closure} }
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